The present invention generally relates to an analyzer for VOCs (Volatile Organic Compounds) in gas and a method of using the same. More particularly, the present invention relates to an on-line analyzer for VOCs in gas and method of using the same.
Volatile Organic Compounds (VOCs) refer to organic chemical compounds that have boiling points roughly in the range of 50° C.-260° C. and saturation vapor pressures above 133.322 Pa on room-temperature conditions. These compounds commonly exist in indoor and outdoor air, and play an import role in increasing tropospheric ozone and generating other oxidants, and may directly produce secondary pollutants, such as organic aerosols. More significantly, some compounds in components of VOCs, such as benzene, 1,3-butadiene etc, have potentially carcinogenic effect. Therefore, it is brought to the attention of the people and becomes an important point of domestic and foreign research, to study the existence, source, distribution regularity and transformation of VOCs in environment and their effect on human health. It is a necessary means for conducting this research to establish a simple and reliable method of sampling and measuring VOCs that have complicated components and extremely small content.
Nowadays, the widely-used methods of analyzing VOCs in air include 1) field sampling-laboratory analysis system and 2) field on-line continuous automatic monitoring system.
The field sampling method of field sampling-lab analyzing system mainly includes bag sampling, stainless steel canister sampling and adsorbent tube sampling. Bag sampling is rarely used now because its inner surface absorbs VOC; stainless steel canister sampling has a well sampling effect, but in this method, it is complex and costly to apply liquid nitrogen to freezingly preconcentrate the sample gas, which needs frequent addition of liquid nitrogen; absorbent tube sampling has some problems, such as low efficiency of absorption and desorption of VOCs, high disturbance of adsorbents and replacement of absorbent tubes and the like. Laboratory analysis methods mainly include gas chromatographic method (GC) (gas chromatographic/hydrogen flame ionization detector/photo-ionization detector) (GC/FID/PID), gas chromatographic/mass-spectrography (GC/MS). In field sampling-laboratory analysis system. The main disadvantage of this system in analyzing VOCs in gas is that it cannot realize real-time continuous automatic monitoring of VOCs in ambient atmospheres and cannot capture the rapid change of concentration of VOCs in air.
At present, analysis principle of the field on-line continuous automatic monitoring system monitoring system mainly involves absorbent tube sampling (room-temperature/low-temperature)/thermal desorption gas chromatography, and the detectors therefor are hydrogen flame ionization detector (FID) and photoionization detector (PID). The main disadvantages of the on-line analyzing system involve problems existing in absorbent tube sampling, such as absorption/desorption efficiencies of different VOCs and replacement of absorbent tubes, both of the two detectors of FID and PID having no specificity for the qualitative analysis of VOCs and having selectivity for the detecting of different VOCs (FID is only used to detect hydrocarbons. PID cannot detect a portion of hydrocarbons C2 and C3, such as ethane and propane, a portion of halogenated hydrocarbons, such as dichloromethane, chloroform, ethylene dichloride and the like, and compounds containing oxygen (nitrogen, sulphur), such as methanol, acrylonitrile, carbonyl sulfide and the like). Therefore, currently, the on-line analyzer for VOCs is mainly used to analyze hydrocarbons C2-C12, and hydrocarbons C2-C5 and hydrocarbons C6-C12 are detected by two analyzers respectively, instead of simultaneously analyzing and detecting hydrocarbons C2-C12, VOCs containing oxygen (nitrogen, sulphur) and halogenated hydrocarbons.
At present, the research on VOCs in ambient atmospheres starts late and the sampling and analyzing of VOCs in air relay on foreign large analytical equipments and instruments, which are costly, complicated in analyzing process and unable to perform real-time on-line continuous automatic analysis, which has a large gap from the actual needs of research of air pollution. Therefore, it is important in a field of atmospheric environment monitoring and research, to seek a new sampling method and analyzing technique of VOCs, develop a analyzer of VOCs with high sensitivity, simple operation, cost-efficient and easy maintenance, and develop a on-line continuous automatic monitoring technique of VOCs.